Squamous cell carcinomas are common forms of cancer, and are found in a variety of organs covered by epithelia. There is increasing evidence implicating inactivation of tumor suppressor genes such as p53 and pRb in epithelial carcinogenesis. The proposed study aims at characterizing the effects of the growth suppressor protein p1O7 on the transcription of c- myc, a gene involved in keratinocyte proliferation. We intend to (i) identify cis-acting elements in the c-myc promoter necessary for inhibition by p107, (ii) identify the p1O7 domains necessary for transcriptional repression, and (iii) compare the effects of p1O7 with those of pRb, a structurally-related tumor suppressor peptide. In addition, we will investigate the effect of tumor viruses such as HPV on transcriptional regulation by p107, and the effects of p1O7 over- expression on proliferation of normal and transformed keratinocytes. Transcriptional studies will be conducted by transfecting reporter genes (GAT or luciferase) driven by deletion- and point-mutants of the human c- myc promoter in a mouse keratinocyte cell line (MK) and in HPV-transformed human keratinocyte lines. The activity of wild-type or mutant p1O7 and pRb will be tested in cotransfection experiments with c-myc constructs. Stable transfectants of MK cells or transformed human keratinocytes will be isolated to study the biological effects of p107 over-expression. The long-term objectives of these studies are to define the role of p107 on epithelial cell proliferation, and to elucidate mechanisms of p107 inactivation by tumor viruses such as HPV.